Combination discs (multilayer optical discs in which a ROM (reproduction-only) layer and a RE (recording and reproducing) layer are mixedly present) are currently in the need. Reasons for this need are for example as follows. In car navigation software, Internet connection cannot be always established, and since it takes time to download all map information, it is preferable to distribute the car navigation software in the form of a low-cost ROM. On the other hand, map information changes daily, so therefore it is preferable that the map information can be updated newly via the Internet. Accordingly, a combination disc which can solve both these problems has been in the need, which combination disc allows for replacing outdated data on the ROM layer with updated data, by recording updated data onto the RE layer while connection to the Internet is available.
In order to obtain the combination disc, it has been considered preferable to provide a ROM layer generally having a higher reflectance than the RE layer, since loss occurs in light returning from an information recording layer (hereinafter, referred to as L0 layer) provided in a farthest position from the reproduction light incident surface, which loss is caused by the presence of other information recording layers, as disclosed in Patent Literature 1.
Moreover, one standard of the optical disc includes a plurality of types such as ROM, R, RW, and RE, and there are various versions (disc types) such as having two layers of the information recording layers to improve recording capacity. Furthermore, on assumption that such combination discs are used for car navigation software as described above, it is preferable that while the car navigation software is not being used, the recording and reproducing apparatus can reproduce rental movie software (ROM) or a disc (R, RW, RE) on which a drama is recorded domestically. Hence, the recording and reproducing apparatus requires having means for identifying a type of the disc as easily as possible, when a disc is loaded therein.
A system in which a barcode is printed outside an information recording area has been considered as the means for identifying the disc type. However, for the reasons described later, it is preferable to record information after the disc has been completed and in a manner such that no correction can be made after addition of the information. Hence, substantially, it is preferable to carry out a recording onto the disc by use of light irradiation, such as BCA recording (recording of information by irradiating an information recording layer with pulse laser light by a YAG laser or the like, whereby forming stripes having for example a width of approximately 10 μm and a length of approximately several hundred μm (as like a barcode)).
Patent Literature 1 discloses a combination disc including a transparent substrate, a RE layer, an intermediate layer, a ROM layer, and a protective resin film, which layers are stacked in this order from a reproduction light incident surface.
In order to obtain a combination disc as like the one disclosed in Patent Literature 1, it is generally preferable to provide a ROM layer having a reflectance higher than that of the RE layer, since loss occurs in light which returns from the information recording layer (L0) that is disposed in the farthest position from the reproduction light incident surface, due to the presence of other information recording layers.
Moreover, Non Patent Literature discloses, as a method of identifying the disc type, a method (BCA) in which information is recorded in the form of recording marks whose size allows the identification of the disc type even in a case where a value of a beam expander and/or a focusing or tracking state are not optimum.